Catalytic cracking of a residuum feedstock to produce lower molecular weight gaseous products

ABSTRACT

The present invention provides a catalytic cracking process. The process includes introducing at least one species of a natural or synthetic residuum containing feedstock and a catalyst into a catalytic cracker reaction zone, and thereafter cracking the feedstock into a lower molecular weight gaseous product and spent cracking catalyst with hydrocarbonaceous product deposited thereon. Among others, the lower molecular weight gaseous product includes ethylene or propylene. The spent cracking catalyst obtained from the catalytic cracker reaction zone may then be regenerated using a first and a second regeneration zone. The first regeneration zone may be operated in an oxidizing mode resulting in a remaining coke of reduced hydrogen content which lowers the moisture content of flue gas in subsequent regeneration zones. The second regeneration zone, may be operated in a partial oxidizing mode and with a controlled carbon dioxide content in the second combustion atmosphere as a reactant with carbon for forming additional carbon monoxide in the flue gas of the second regeneration zone.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. patentapplication Ser. No. 10/413,728, entitled “A METHOD OF PRODUCINGSYNTHESIS GAS FROM A REGENERATION OF SPENT CRACKING CATALYST,” filed onApr. 15, 2003, which is a continuation-in-part of U.S. application Ser.No. 10/272,709, entitled “METHOD OF PRODUCING SYNTHESIS GAS FROM AREGENERATION OF SPENT CRACKING CATALYST,” filed on Oct. 17, 2002, whichis a continuation-in-part of U.S. Pat. No. 6,491,810, entitled “METHODOF PRODUCING SYNTHESIS GAS FROM A REGENERATION OF SPENT CRACKINGCATALYST,” filed on Nov. 1, 2000, and issued on Dec. 10, 2002. Theabove-listed applications are commonly assigned with the presentinvention and are incorporated herein by reference as if reproducedherein in its entirety.

TECHNICAL FIELD OF THE INVENTION

[0002] The present invention is directed, in general, to a method ofusing a catalytic cracker and, more specifically, to a process forcatalytically cracking residuum feedstock to produce lower molecularweight gaseous products.

BACKGROUND OF THE INVENTION

[0003] Catalytic cracking processes have been developed principally forupgrading feedstock derived from natural or synthetic crude oil to morevaluable hydrocarbon mixtures, particularly of lower molecular weight.These lower molecular weight hydrocarbons are generally more desirablebecause of their higher quality and market value. In a typical catalyticcracking process, a crude oil derived feedstock is contacted with a hot,regenerated catalyst, at temperatures ranging from about 1200° F. toabout 1400° F. and low to moderate pressures. The chemical reactionsthat take place in the presence of the catalyst include predominantlyscission of carbon-to-carbon bonds (simply cracking), isomerization,polymerization, dehydrogenation, hydrogen transfer, and others,generally leading to lower molecular weight hydrocarbon products.

[0004] Some of the cracking reactions in the catalytic cracker alsoproduce hydrocarbonaceous compounds of high molecular weight, of verylow volatility, of very high carbon content and of low combined hydrogencontent. The hydrocarbonaceous compounds tend to be deposited on theactive surfaces of the cracking catalyst and mask the active sites,rendering the catalyst less active, thus unsuitable for continuedcracking without regeneration. Deposits of the hydrocarbonaceous matterand the inclusion of absorbed and adsorbed hydrocarbons, as well as thevaporous combustible components in the fluidizing media between thesolid catalyst particles, collectively called “coke,” are in a senseundesirable. In response to the undesirable buildup of coke on thesurfaces of the catalyst, the oil and gas industry has developed severaltechniques to reduce or remove such buildups.

[0005] One technique currently used to reduce the coke formingcharacteristics of feedstocks, includes without limitation,hydrotreatment, distillation, or extraction of the natural or syntheticcrude feedstock prior to charging it to the catalytic cracker.Hydrotreatment, distillation, or extraction of the crude oil derivedfeedstock serves to remove a substantial amount of the coke precursors,such as contained in asphaltenes, polynuclear aromatics, etc., prior tocatalytic cracking. Hydrotreatment, distillation, or extraction aresomewhat effective in reducing or removing large amounts of cokeprecursors from the crude oil derived feedstock, however, such processesare expensive and time-consuming. Currently, incrementally availablecrude oil is of high residuum content and of higher coke formingcharacteristics at a time when it is unpopular or unlawful to utilizethis additional residuum as fuel oil. At the same time, the market forresiduum products, other than as fuel oil, is saturated. Additionally,to upgrade the residuum materials by the available technology results inproducts of lower quality (and lower market value) than would beachieved by catalytic cracking, provided the coke yield can be handled.Moreover, current and anticipated Federal and State legislation has, andis, scrutinizing the environmental and storage issues associated withuse, removal or conversion of the coke precursors. Therefore, there is agreat need for an environmentally responsible conversion of the residuumportion of crude oil.

[0006] Another technique currently used to remove coke formation fromthe spent cracking catalyst is to burn the coke away from the catalystsurface using an oxygen-containing gas stream in a separate regenerationreactor. In such a situation, air, oxygen, carbon dioxide, and steam fordiluent as combustion gas, may be introduced into the spent crackingcatalyst in the lower portion of the regeneration zone(s), whilecyclones are provided in the upper portion of the regeneration zone forseparating the combustion gas from the entrained catalyst particles. Thecoke buildup removal process attempts to substantially remove the cokebuildup, and is generally effective, but large amounts of greenhousegases are produced, at least some of which are released into theatmosphere, which is generally environmentally undesirable. Anothertechnique teaches the use of a waste heat boiler as a means of reducinggreenhouse gases going to the atmosphere, however, the reduction by thismethod remains limited to the achievable concentration of a firedheater. In each of the aforementioned techniques the initialregeneration zone is operated in a partial oxidizing (reducing) mode,and any other regeneration zone is operated in an oxidizing mode. U.S.Pat. No. 4,388,218 entitled “Regeneration of Cracking Catalyst in TwoSuccessive Zones” to Rowe, and U.S. Pat. No. 4,331,533 entitled “Methodand Apparatus for Cracking Residual Oils” to Dean et al., further detailsuch processes and are included herein by reference.

[0007] Similarly, the regeneration zone must be carried out in such away that it is in thermal equilibrium with the cracking reaction zone.In other words, the sensible heat of the hot regenerated catalyst in thecatalytic cracker should be in balance with the heat requirements of thecatalytic cracking reactor zone. In conventional operations, excludingthe use of internal or external cooling coils for removing heat from theregenerator reaction zone, coke yield of only about 5 to about 8 weightpercent of the total feed may be burned from the catalyst, withoutexceeding the amount of heat required to balance and sustain thecracking reaction.

[0008] Thus, to maintain the thermal balance needed to operate thecatalytic cracker and remove enough of the coke from the catalyst tosustain the cracking process, one of two things should be done. First,the amount of coke that forms on the surface of the catalyst should bereduced. However, as mentioned above, this can typically be accomplishedby using higher quality feedstock, which is more costly, or subjectingthe currently available feedstock to the previously mentioned upgrading,such as but not limited to, hydrotreatment, distillation or extractionprocesses, which are also more costly. Second, internal or externalcooling units could be installed in the regeneration units. However,such internal or external cooling units are costly and unreliable.

[0009] Accordingly, what is needed in the art is a method ofcatalytically cracking crude oil derived feedstock having high cokeforming characteristics, without experiencing the drawbacks of the priorart methods.

SUMMARY OF THE INVENTION

[0010] To address the above-discussed problems of the prior art, thepresent invention provides a catalytic cracking process. The processincludes introducing at least one species of a natural or syntheticresiduum feedstock and a catalyst into a catalytic cracker reactionzone, and thereafter cracking the feedstock into a lower molecularweight gaseous product and spent cracking catalyst withhydrocarbonaceous product deposited thereon. The spent cracking catalystobtained from the catalytic cracker reaction zone may then beregenerated. In one embodiment, the spent cracking catalyst isregenerated by introducing the spent cracking catalyst into a firstregeneration zone in a presence of a first atmosphere comprising a firstoxygen containing gas at a first regeneration temperature. For example,a temperature that does not exceed about 1400° F., and more preferable,a temperature that ranges from about 1150° F. to about 1400° F., may beused as the first regeneration temperature. The first regeneration zoneoxidizes a greater proportion of a hydrogen content than carbon contentof coke associated with the spent cracking catalyst, therebysubstantially reducing a water content of a subsequent regenerationzone, thereby reducing cracking catalyst damage resulting from the hightemperature regeneration with a high moisture content atmosphere.

[0011] The method further includes introducing the spent crackingcatalyst from the first regeneration zone into a second regenerationzone. The spent cracking catalyst is introduced into the secondregeneration zone in a presence of a second atmosphere comprising asecond oxygen containing gas and carbon dioxide, and at a secondregeneration temperature substantially greater than the firstregeneration temperature. For example, the second regeneration zone maybe operated at a temperature ranging from about 1500° F. to about 1800°F. and maintained in a partial oxidation mode. In such an instance, thesecond atmosphere, the second regeneration zone temperature and thepartial oxidation mode of operation results in a substantial portion ofthe carbon dioxide of the second atmosphere to function as a reactantwith carbon content of the coke remaining associated with the spentcracking catalyst to form two moles of carbon monoxide per mole ofcarbon dioxide reacted, and thus result in a synthesis gas product richin carbon monoxide.

[0012] In contrast to the prior art catalytic cracking method, theabove-mentioned method is capable of producing commercial amounts ofsynthesis gas, which may then be commercially used or sold. Moreover,the above-mentioned method is capable of accepting feedstock having highcoke forming characteristics, which in one advantageous embodiment, maybe accepted without hydrotreating, separating as a distillation overheadproduct, or solvent extracting as an extract product the feedstock priorto catalytic cracking. Both the ability to accept, and the ability toaccept without the need for hydrotreating, distillation, or solventextraction, provide both economical and environmental benefits notachieved in the prior art methods.

[0013] In another aspect of the invention, the synthesis gas comprisescarbon monoxide. Where the amount of synthesis gas produced isinadequate to meet the market needs or the intended system consumptioncapacity, in an alternative aspect, a supplemental fuel, such as ahydrocarbonaceous material, may be introduced into the spent catalystflow path through the regeneration zones. Preferably this is added at ornear the entrance to the first regeneration zone, in order that thecombined hydrogen content will be reduced in the first regenerationzone, thus subsequent regeneration zones will have reduced waterformation therein. The supplemental fuel is preferably one of lowhydrogen content and is preferably introduced into the firstregeneration zone.

[0014] The foregoing has outlined preferred and alternative features ofthe present invention so that those skilled in the art may betterunderstand the detailed description of the invention that follows.Additional features of the invention will be described hereinafter thatform the subject of the claims of the invention. Those skilled in theart should appreciate that they can readily use the disclosed conceptionand specific embodiment as a basis for designing or modifying otherstructures for carrying out the same purposes of the present invention.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] For a more complete understanding of the present invention,reference is now made to the following descriptions taken in conjunctionwith the accompanying drawing, in which:

[0016]FIG. 1 illustrates one embodiment of a catalytic cracking systemwherein the inventive method may be practiced; and

[0017]FIG. 2 illustrates an alternative embodiment of a catalyticcracking system having a third regeneration zone wherein the inventivemethod may be practiced.

DETAILED DESCRIPTION

[0018] The embodiments of the present invention, among other things,teach the catalytic cracking of residuum feedstock to a crackingseverity sufficient to maximize a product rich in ethylene andpropylene. In contrast, the prior art only teaches the catalyticcracking of a gas oil type feedstock to produce low molecular weightproducts such as one rich in ethylene and uses catalyst coolingequipment in the regeneration section to maintain the heat balancebetween the heat release of the regeneration zone(s) and the heatrequirements of the cracking reaction zone(s). The prior art, however,does not teach the use of a feedstock of high coke formingcharacteristics, such as without significant limitations, residuumfeedstock to produce lower molecular weight product, such as withoutlimitations ethylene, without using heat removal from the spent catalystregeneration zone(s).

[0019] The customary feedstock in the thermal cracking prior art forproducing such products as ethylene includes: 1) LPGs such as ethane andpropane, 2) naphtha, 3) condensate, or components thereof. The prior artalso teaches the use of residuum feedstock for coking, but the yieldpotential of lower molecular weight component is not significant becausesuch prior art produces mostly coker gasoline, middle distillate, fueloil, and petroleum coke, generally of high sulfur content and thepetroleum coke must compete with coal (on a calorific and sulfur contentbasis) in the market place. This equipment also, must have much parallelequipment to maintain on stream time.

[0020] In contrast, the embodiments disclosed herein facilitate a steadystate design for continuous, sustained operability without parallelequipment for not only cracking, but highly selective catalytic crackingwith well developed and selective, prior art catalyst and wherein thecoke (hydrocarbonaceous portion) of the product is deposited on thecatalyst within the cracking reaction zone(s) and may be removed fromthe cracking reaction zone with the spent cracking catalyst.

[0021] The catalytic cracking of feedstock of high coke formingcharacteristics, such as without limitations, residuum feedstock usingthe prior art teaching has been limited, for the most part, to a productof gasoline and higher boiling range components and managing theexcessive coke formation by operating catalyst cooling coils as a meansof managing the excessive coke formation by operating catalyst coolingcoils. In the embodiments of the present invention, however, cokeproduction in excess of that needed to sustain heat balance betweenregeneration zone and the cracking reaction zone is accommodated byintroducing a carbon dioxide rich stream as a reactant to chemicallyreact with the carbon content of the coke endothermically, thuscontrolling the regeneration reactions net heat release.

[0022] Accordingly, before the present invention, all the art failed toshow a continuous process for regenerating the spent cracking catalystwithout removal of excess heat of regeneration in such as internal orexternal cooling coils. In the herein disclosed invention feedstock ofhigh coke forming characteristics may be catalytically cracked atcracking severity sufficient to maximize lower molecular weight product,such as without limitations ethylene, and then regenerate the heretoforeunmanageable high coke yield, producing therefrom a synthesis gas richin carbon monoxide content while preserving the integrity of prior artcatalyst. In one embodiment, a second species of catalyst, effective inpromoting partial oxidizing reactions, is used in mixture with the spentcracking catalyst, at least in the second regeneration zone which isoperated in partial oxidization mode, and carbon dioxide as a reactantwith carbon of the coke.

[0023] As used herein, the term residuum feedstock means a hydrocarbonmaterial of natural or synthetic origin with characteristics of 1)containing compounds of high molecular weight, 2) low volatility, 3)relatively high carbon content, 4) relatively lower hydrogen content, 5)relatively high in metallic compounds such as, but without limits, iron,nickel, vanadium. Included within the above meaning of ResiduumFeedstock would be a) long residuum, b) short residuum, c) tar, d)pitch, e) asphalt, f) or shale oil residuum.

[0024] As also used herein, the term lower molecular weight gaseousproduct (at least the major portion of which would be in a gaseous phaseat ambient temperature and pressure) includes, without limitations,ethylene, ethane, propylene, propane, butylenes, and butanes.

[0025] Referring now to FIG. 1, illustrated is a schematic diagram of anexemplary configuration of a catalytic cracking system 100, inaccordance with the present invention. In the illustrative embodimentshown in FIG. 1, the catalytic cracking system 100 includes a catalyticcracking reaction zone 200, a first regeneration zone 300 and secondregeneration zone 400. Those skilled in the art will understand that thecatalytic cracking reaction zone 200, first regeneration zone 300 or thesecond regeneration zone 400 may include a contact system other than thedilute phase (entrained) flow section shown in FIG. 1, there being othercracking reaction zone and/or regeneration zone designs suitable for usewith the disclosed invention. Likewise, those skilled in the art willalso understand that the present invention is not limited to a singlecatalytic cracking reaction zone 200 and two regeneration zones 300,400. Multiple cracking reaction zones and regeneration zones are withinthe scope of the present invention. (FIG. 2—discussed infra). It shouldalso be noted that certain valves, flanges, fittings, and someassociated pumps, exchangers, instruments, etc., may not be shown inFIG. 1 for simplicity reasons.

[0026] In the illustrative embodiment shown in FIG. 1, the catalyticcracking reaction zone 200 includes a cracker reactor disengaging space210, a spent catalyst steam stripper 220, a dilute phase crackingreactor transport line 230 and a cracked product exit transport line240. The catalytic cracking reaction zone 200 may also, in an exemplaryembodiment, include cyclones 250. In the embodiment illustrated in FIG.1 the cyclones 250 are shown as a single cyclone, however, it should benoted that there may be more than one cyclone in parallel, or evengroups of cyclones in series or in series and in parallel. It should benoted that the cyclones for the catalytic cracking reaction zone 200,the first regeneration zone 300 or the second regeneration zone 400 areshown as internal cyclones, but may be externally mounted withoutchanging the teaching of this disclosed invention.

[0027] The catalytic cracking reaction zone 200 in the embodiment shownin FIG. 1 is a dilute phase fluid bed catalytic cracker, but thoseskilled in the art will understand that the fluid bed catalytic crackermay be replaced with a moving bed catalytic cracker, falling bedcatalytic cracker, fixed bed catalytic cracker, or any other known orhereafter discovered catalytic cracker, without departing from the scopeof the present invention. Also, in an advantageous embodiment, thecatalytic cracking reaction zone 200 is designed to crack residuumfeedstock (including virgin residuum feedstock) and recycled hydrocarbonfeedstock at an optimum cracking temperature for a desired end product.Those skilled in the art understand that separate cracking reactionzones may be provided to allow separate optimum cracking conditions forseparate feedstock.

[0028] In the illustrative embodiment shown in FIG. 1, the firstregeneration zone 300 includes a first disengaging space 310, a firstpartially regenerated catalyst transport line 320, a first regeneratordilute phase transport line 330 and a first regeneration zone flue gastransport line 340. Similar to the catalytic cracking reaction zone 200,the first regeneration zone 300 may, in a preferred embodiment, includecyclones 350. In the embodiment shown in FIG. 1, two cyclones 350 areshown in series, however, it should be noted that one or more cyclones,internal, external or a mixture of such, in series, parallel, or both,are also within the scope of the present invention. The firstregeneration zone 300 may also include a first regeneration zonetreating or separation system 360. Any one or combination of knowntreating or separation processes may be used, for example withoutlimitation, removal of water, sulfur oxide (SO_(x)), nitrogen oxide(NO_(x)) and carbon monoxide (CO). The first regeneration zone 300 shownin FIG. 1 may further include a carbon dioxide stripper 315. The carbondioxide stripper 315, as illustrated, is located between the firstdisengaging space 310 and the first partially regenerated catalysttransport line 320, and is configured to displace components, such aswithout limitation nitrogen and argon, which would otherwise contaminatethe synthesis gas product of the second regeneration zone 400.

[0029] In the illustrative embodiment shown in FIG. 1, the secondregeneration zone 400 includes a second disengaging space 410, aregenerated catalyst transport line 420, a second regenerator dilutephase transport line 430 and a second regeneration zone flue gastransport line 440. Similar to the catalytic cracking reaction zone 200,the second regeneration zone 400 may, in a preferred embodiment, includecyclones 450. In the embodiment shown in FIG. 1, two cyclones 450 areshown in series, however, it should be noted that one or more cyclones,internal, external or a mixture of such, in series, parallel, or both,are also within the scope of the present invention. The secondregeneration zone 400 may also include a second regeneration zonetreating or separation system 460, wherein the second regeneration zonetreating or separation system 460 is similar to the first regenerationzone treating or separation system 360. Those skilled in the art willrealize that other types of catalytic cracking system 100 designs maysatisfy the requirements of the present invention without changing theteachings disclosed herein, for example without limitations, includingusing multiple cracking or regeneration reaction zones, with common orseparate disengaging spaces, instead of that illustrated in FIG. 1.

[0030] It has been found that typical oxidizing reactions proceed morerapidly at higher temperatures. However, it has also been found thateach individual oxidizing reaction rate disproportionately changes withtemperature. To understand such a process, the following oxidizingreactions have been provided:

[0031] (1) C+{fraction (1/2)}O₂=CO;

[0032] (2) C+O₂=CO₂;

[0033] (3) C+CO₂=2CO;

[0034] (4) C+H₂O=CO+H₂; and

[0035] (5) C+2H₂O=CO₂+2H₂.

[0036] It has further been found that the reaction rate (change in areactants concentration as a function of time) for reaction (1)increases more rapidly with increased temperature than does reaction(2). At temperatures below 1400° F. the equilibrium molal ratio ofCO/CO₂ is well below unity, where at temperatures near 1800° F. theCO/CO₂ molal ratio is much greater. By limiting oxygen input such thatthere is little or no excess oxygen at temperatures ranging between thecracking reactor temperature and about 1400° F. the formation of CO₂ isfavored. At temperatures between about 1400° F. and about 1800° F. theformation of CO is favored and the oxidization is rapid.

[0037] It has also been found that even the most thermally stablecracking catalyst commercially used is stable up to a temperature ofonly about 1400° F. in the presence of the water vapor content normallyexperienced in regenerating the cracking catalyst. Furthermore, it hasbeen found that such commercially used cracking catalysts may besubjected to temperatures up to about 1800° F. in contact with oxidizinggas (flue gas) of decreased water content, the allowable water contentbeing somewhat inversely proportional to temperature.

[0038] It is further known that the reaction rate of reaction (3) isalmost nonexistent at or below temperatures of about 1400° F., butbecomes significant between about 1400° F. and about 1800° F. From thesefacts, it has been found that the most favorable method of regeneratinga cracking catalyst to produce carbon monoxide (CO) is to first oxidizeonly enough of the coke as to reduce the concentration of combinedhydrogen in the coke, the hydrogen containing compounds being morerapidly oxidized than the resulting elemental carbon content, especiallythe elemental hydrogen or low molecular weight fuel, such as but notlimited to methane. After having reduced the hydrogen content of thecoke in the first regeneration zone 300, the remainder of the carbon ofthe coke in a second regeneration zone 400 (and possibly a thirdregeneration zone 500, as subsequently shown in FIG. 2) may be oxidizedat a higher temperature without damage to the catalyst because of thereduced moisture content.

[0039] Turning briefly now to FIG. 2, illustrated is an alternativeembodiment of the invention depicting a catalytic cracking system 105having a third regeneration zone 500. It is to be noted that theelements of the embodiment illustrated in FIG. 2, and their description,are similar to that shown and described in FIG. 1, with the exceptionthat the catalytic cracking system 105 of FIG. 2 also includes the thirdregeneration zone 500. Additionally, instead of the fully regeneratedcracking catalyst flow from the second regeneration zone 400 returningto the catalytic cracking reaction zone 200, as shown in FIG. 1, in FIG.2 a less than fully regenerated cracking catalyst is directed from thesecond regeneration zone 400 to a third regeneration zone 500.

[0040] As is illustrated in FIG. 2, the third regeneration zone 500includes a third disengaging space 510, a regenerated catalyst transportline 520, a third regenerator dilute phase transport line 530, and athird regeneration zone flue gas transport line 540. Similar to thecatalytic cracking reaction zone 200, the third regeneration zone 500may, in a preferred embodiment, include cyclones 550. In the embodimentshown in FIG. 2, two cyclones 550 are shown in series, however, itshould be noted that one or more cyclones, either internal, external ora mixture of such, in series, in parallel, or both, are within the scopeof the present invention. The third regeneration zone 500 may alsoinclude a third regeneration zone treating or separation system 560.

[0041] Also shown in FIG. 2 is a unique feature of utilizing a secondspecies of a catalyst effective in promoting partial oxidizingreactions. The second species of catalyst is for the most part, but notabsolutely, confined to the regeneration zones 300, 400, 500. It may benoted that in FIG. 2, as in FIG. 1, a carbon dioxide stripper 315 mayalso be utilized to displace by stripping action certain componentscontained in the fluidizing media of the partially regenerated spentcatalyst flowing from the first regeneration zone 300 to the secondregeneration zone 400. For example, where air or oxygen enriched air isused in the first regeneration zone 300, the carbon dioxide stripper 315may be used to displace nitrogen and argon, among others.

[0042] With reference again back to the embodiment illustrated in FIG.1, the discussion will now turn to specific details of a method of usingthe catalytic cracking system 100, or another similar system, to producea commercial quality and amount of a synthesis gas while regenerating aspent cracking catalyst. Initially a feedstock 610 is supplied to alower portion of the dilute phase cracking reactor transport line 230where it is combined with regenerated catalyst provided from theregenerated catalyst transport line 420. The feedstock 610, in anexemplary embodiment, includes at least one species of a natural orsynthetic residuum feedstock. Similarly, the feedstock 610 may includevirgin residuum feedstock. In another embodiment, the feedstock 610comprises a fresh feed stream combined with a recycled hydrocarbonstream and a controlled amount of initial fluidizing and dispersingmaterial, such as gas, hydrogen, or steam. Those skilled in the art willunderstand the desire to avoid contact between steam and the regeneratedcatalyst at temperatures about 1400° F. Moreover, prior to entering thelower portion of the dilute phase cracking reactor transport line 230,the feedstock 610 may be preheated in a furnace 620. The furnace 620 mayprovide for a controlled increase in the temperature of the feedstock610, or vaporization of at least a part thereof, which may facilitatethe cracking reaction of the feedstock 610 in contact with theregenerated catalyst provided from the regenerated catalyst transportline 420. It should be noted, and is well understood by one skilled inthe art, that the feedstock 610 flowing through the furnace 620 forpreheating, may include at least portions of recycled hydrocarbon streamand initial fluidizing and dispersing material through piping not shown,and that the feedstock 610 could include other similar materials. In oneparticularly advantageous embodiment, the fresh feed stock streamcomprises a high coke forming feedstock, such as an unseparatedfeedstock containing high amounts of asphalt and pitch. As mentionedabove, the feedstock 610 may comprise at least one species of a naturalor synthetic residuum feedstock. As previously mentioned, the feedstockmay be preheated in the furnace 620, however, in an alternativeembodiment, the feedstock 610 may be bypassed around the furnace 620,using lines not shown herein.

[0043] After entering the lower portion of the dilute phase crackingreactor transport line 230 and combining with the regenerated catalystfrom the regenerated catalyst transport line 420, the hydrocarbons reactto form reactants and coke, and the mixture rises to the upper portionof the dilute phase cracking reactor transport line 230. The mixture maythen discharge from the upper portion of the dilute phase crackingreactor transport line 230 into the cracker reactor disengaging space210, where cracking reactions continue. As is understood by one skilledin the art, the cracking process produces vaporous cracked material andspends cracking catalyst by depositing coke thereon. Once within thecracker reactor disengaging space 210, vaporous cracked material risesto the upper portion of the cracker reactor disengaging space 210. Inthis embodiment, the vaporous cracked material rises to the upperportion of the cracker reactor disengaging space 210 and enters one or aplurality of the cyclones 250. The cyclones 250 tend to separate thevaporous cracked material from any remaining spent catalyst suspendedtherein. The vaporous cracked material may then rise and exit throughthe cracked product exit transport line 240 and then flow to separationequipment (not shown). The spent catalyst removed by the cyclones 250may then flow downwardly and discharge from a dip leg of the cyclones250.

[0044] The vaporous cracked material, in an exemplary embodiment,comprises a lower molecular weight gaseous product. For example, anumber of lower molecular weight gaseous products, such as products richin olefin content, rich in ethylene content, and rich in propylenecontent. (The term “rich” as used with respect to the olefin, ethyleneor propylene content, refers to a quantity and quality of those contentsthat may be competitively obtained and sold, in one embodiment of theinvention.) Other lower molecular weight gaseous products are, however,within the broad scope of the present invention.

[0045] The spent catalyst may then flow from the lower portion of thecracker reactor disengaging space 210 to the spent catalyst steamstripper 220. In the illustrative example shown in FIG. 1, the spentcatalyst flows downwardly as steam countercurrently flows upwardly. Thesteam may be provided using a steam input transport line 630, andalternatively may be superheated, up to a temperature of about 1400° F.,prior to entering the spent catalyst steam stripper 220. Depending onthe design of the spent catalyst steam stripper 220, the upward flowingsteam may flow from the spent catalyst steam stripper 220 to the lowerportion of the cracker reactor disengaging space 210, or the upwardflowing steam may alternatively be withdrawn using a steam seal, pipingand valve that is not shown.

[0046] Spent and steam stripped, the spent cracking catalyst may flowfrom the catalytic cracking reaction zone 200, through a carriertransport line 640, to the first regeneration zone 300. In a morespecific example, the spent cracking catalyst may enter the lowerportion of the first regenerator dilute phase transport line 330. At thelower portion of the first regenerator dilute phase transport line 330,the spent cracking catalyst may be introduced to a first atmospherecomprising a first oxygen containing gas. The first oxygen containinggas comprises a first combustion gas in one embodiment of the invention.For example, the first oxygen containing gas could be air, oxygenenriched air, or another similar oxygen containing gas. Oxygen enrichedair may be created using a number of different techniques. In a firsttechnique, oxygen enriched air could be created by adding commerciallypure oxygen to air. In another technique, oxygen enriched air could becreated by reducing one or more non-oxygen components therefrom, such aswithout limitations, nitrogen or argon. Any known or hereafterdiscovered means, such as without limitation, membrane permeation,selective adsorption, partial condensation, flash distillation, etc.,could be used to reduce the concentration of aforementioned non-oxygencomponents.

[0047] In a preferred embodiment, the first atmosphere, or componentsthereof, may be preheated, for example without limitation, in a furnace650 prior to combining with the spent cracking catalyst. In anotherpreferred embodiment, the furnace 650 preheats the first atmosphere to atemperature substantially equal to the operating temperature of thefirst regeneration zone 300. The components of the first atmosphere areshown in FIG. 1 as flowing into a common transport line prior toentering the lower portion of the first regenerator dilute phasetransport line 330, however, the skilled artisan will understand thatany one or any portion of these flows may be introduced through furnace650 separately or in any combination. Although the preheating of thefirst atmosphere is shown herein as being accomplished with a furnace650, the preheating may be accomplished by any means without changingthe teachings of this disclosed invention.

[0048] The amount of the first oxygen containing gas may vary, however,the amount of the first oxygen containing gas should be adjusted so asto oxidize a minimal portion of the net coke and supplemental fuel, ifany, but to reduce the hydrogen content of the coke and supplementalfuel if any associated with the spent cracking catalyst leaving thefirst regeneration zone 300, yet while raising the temperature of thisfirst regeneration zone 300 to initiate partial oxidizing reactions inthe following second regeneration zone 400. In one advantageousembodiment, the amount of each gas component should be controlled toachieve a first regeneration zone 300 temperature not to exceed about1400° F., and more precisely, a first regeneration zone 300 temperatureranging from about 1150° F. to about 1400° F. Regeneration temperaturesabove about 1400° F., in the presence of anticipated waterconcentration, like provided in the first regeneration zone 300, aregenerally undesirable since they tend to cause damage to the crackingcatalyst.

[0049] The spent cracking catalyst and the first oxygen containing gasflow upwardly within the first regenerator dilute phase transport line330 to the first disengaging space 310 for separation of vaporousreactants from the spent cracking catalyst. Partially regeneratedcatalyst flowing from the upper portion of the first regenerator dilutephase transport line 330 tends to fall into the lower portion of thefirst disengaging space 310 to form a fluid bed. While located withinthe fluid bed, additional oxidation of the coke from the partiallyregenerated catalyst may occur. To facilitate the additional oxidationwithin the fluid bed, in an exemplary embodiment, additional amounts ofthe first oxygen containing gas of like or different composition may beintroduced within the fluid bed. For example, the additional amounts ofthe first oxygen containing gas may be introduced within the lowerportion of the fluid bed through a distribution grid or piping coil, notshown.

[0050] The vaporous reactants of the first regeneration zone 300 tend torise within the first disengaging space 310 and enter cyclones 350. Thecyclones 350, similar to the cyclones 250 described above with respectto the catalytic cracking reaction zone 200, may separate suspendedspent catalyst from the vaporous reactant's flue gas. Spent catalystremoved from the vaporous flue gas within cyclones 350 flows downwardlythrough the dip leg to the fluid bed, as the vaporous flue gas exits thefirst regeneration zone 300 through the first regeneration zone flue gastransport line 340. In one advantageous embodiment, the vaporous fluegas then enters the first regeneration zone treating or separationsystem 360. The vaporous flue gas may be given treatment or separationutilizing any one or more of several types of well-known treatments.Such treatments or separation may separate the vaporous flue gas intoits constituent components consistent with its intended use. Attemperatures ranging from about 1150° F. to about 1400° F., the mostrapid components to oxidize are those which contain hydrogen content,sulfur content and nitrogen content, however, carbon dioxide content,carbon monoxide content and other pollutants are also present in theflue gas. In one particularly advantageous embodiment, the carbondioxide content of the flue gas by-product of the first regenerationzone 300, with or without separation treatment as described above, mayprovide at least a portion of the carbon dioxide needed in the first orsecond regeneration zones 300, 400, or in the carbon dioxide stripper315, described in more detail below.

[0051] A portion of the hot partially regenerated spent catalyst locatedwithin the fluid bed may be recycled through a transport line 380 to thelower portion of the first regenerator dilute phase transport line 330.This flow may be used to increase the initial combined temperature andthus accelerate the initial oxidizing reaction rate in the firstregenerator dilute phase transport line 330. However, the net crackingcatalyst portion of the partially regenerated spent catalyst travelsfrom the first disengaging space 310 to the second regeneration zone400. In a preferred embodiment, the remaining portion of the partiallyregenerated spent catalyst travels through the first partiallyregenerated catalyst transport line 320 to a lower portion of the secondregenerator dilute phase transport line 430.

[0052] Those skilled in the art will realize that partially regeneratedspent cracking catalyst flowing from the first regeneration zone 300will carry with it into the second regeneration zone 400 dilutingcomponents of the first oxygen containing gas, if present, such aswithout limitation nitrogen and argon where air or some forms of oxygenenriched air is used as the first oxygen containing gas in thefluidizing media between the catalyst particles. In a preferredembodiment shown in FIG. 1, the partially regenerated spent crackingcatalyst is stripped with gaseous carbon dioxide rich stream of lowmoisture content (preferably less than 1 mole percent moisture) thusreplacing the diluting components, such as without limitations, nitrogenand argon which would otherwise appear in the synthesis gas productdescribed below. In such a stripping process, the partially regeneratedspent cracking catalyst from the lower portion of the first disengagingspace 310 flows into the carbon dioxide stripper 315 where the catalystis contacted with rising carbon dioxide containing stream introducedthrough carbon dioxide transport line 325. The carbon dioxide containingstream rises in the carbon dioxide stripper 315 while partiallyregenerated spent cracking catalyst flows downwardly as fluidizing mediabetween the catalyst particles and in the void space thereof, isreplaced with carbon dioxide containing stream. The stripped, partiallyregenerated, spent cracking catalyst then flows via the first partiallyregenerated catalyst transport line 320, to the second regeneratordilute phase transport line 430.

[0053] At the lower portion of the second regenerator dilute phasetransport line 430, the partially regenerated spent cracking catalystfrom the first partially regenerated catalyst transport line 320 isintroduced to a second atmosphere comprising a second oxygen containinggas and a carbon dioxide containing stream. In a preferred embodiment,the second atmosphere comprises a combustion gas. The partiallyregenerated spent cracking catalyst and the second atmosphere, in anexemplary embodiment, are substantially water-free. For example, inanother exemplary embodiment, flue gas from the regeneration of thepartially regenerated spent cracking catalyst along with the secondatmosphere, have a water content ranging from about 1 to about 10 molepercent.

[0054] As used herein, oxygen includes commercially available pure, orinternally produced pure oxygen. As also used herein, the carbon dioxidecontaining stream includes, without limitation, pure carbon dioxide aswell as carbon dioxide rich gas. Preferably, the carbon dioxide rich gascomprises in excess of about 50 mole percent carbon dioxide, and evenmore preferably, in excess of about 75 mole percent carbon dioxide. Itshould be noted, however, that the present invention is not limited tosuch percentages.

[0055] In one particularly advantageous embodiment, the carbon dioxidecontent of the flue gas by-product of the first regeneration zone 300may provide at least a portion of the carbon dioxide containing streamneeded in the second regeneration zone 400 and/or the carbon dioxidestripping of the partially regenerated spent cracking catalyst. In analternative embodiment the carbon dioxide rich flue gas of the thirdregeneration zone 500 (FIG. 2), if used, may be used in any one or anycombination of the oxygen containing atmospheres or the carbon dioxidestripping of partially regenerated spent cracking catalyst that it mightbe required, and may be at least partially utilized in its naturallyoccurring hot, relatively dry state. In a preferred embodiment, thesecond atmosphere, or strictly the carbon dioxide containing streamportion of the atmosphere, may be preheated in a furnace 670 prior to orafter combining with the oxygen containing gas and the spent crackingcatalyst. Similar to the furnace 650, the furnace 670 may preheat thesecond atmosphere, or strictly the carbon dioxide containing streamportion of the atmosphere, to a temperature substantially equal to theoperating temperature of the second regeneration zone 400. Those skilledin the art will also realize that the preheating of the secondatmosphere, or strictly the carbon dioxide containing stream portion ofthe atmosphere, may also be accomplished by heat exchange with a hotprocess stream. The hot process stream, in an exemplary embodiment,could include the first regeneration zone flue gas transport line 340 orthe second regeneration zone flue gas transport line 440. The secondatmosphere, or strictly the carbon dioxide containing stream portion ofthe atmosphere, is preferably preheated because it has been found thatthe carbon dioxide will not begin to react with the carbon of the cokesignificantly until the temperature is greater than about 1400° F., butat such temperature it reacts endothermically to form more carbonmonoxide at a decreasing temperature, thus limiting the second reactortemperature in the second regeneration zone 400. The components of thesecond atmosphere are shown in FIG. 1 as flowing into a common transportline prior to entering the lower portion of the second regeneratordilute phase transport line 430, however the skilled artisan willunderstand that any one or a portion of these flows may be introducedseparately or in combination.

[0056] The flow rate of each component of the second atmosphereintroduced to the second regeneration zone 400 may vary, however, theflow rate of each component should be adjusted independently so as tooxidize a substantial portion of the remaining net coke production, yetoperate in a partial oxidizing mode. In one advantageous embodiment, theamount of each component should be controlled individually to achieve asecond regeneration zone 400 temperature substantially greater than thefirst regeneration zone 300 temperature, and to achieve optimumconversion of the coke and supplemental fuel to carbon monoxide. Forexample, the second regeneration zone 400 temperature should be greaterthan the maximum of 1400° F. used in the first regeneration zone 300. Inan exemplary embodiment, the second regeneration zone 400 temperaturemay range from about 1500° F. to about 1800° F. Since the water forminghydrogen content of the coke was substantially reduced in the firstregeneration zone 300, the partially regenerated spent cracking catalystcan handle temperatures up to about 1800° F. without damage, which iscontrary to the first regeneration zone 300, and contrary to the priorart carbon monoxide (synthesis gas) forming regenerators. Generally, theheat generated in the second reaction zone 400 is desirable for thereaction and should remain therein. For example, in a preferredembodiment the first and second regeneration zones 300, 400,respectively, should not have a significant amount of heat removed,because to do so could suppress the endothermic reaction of carbondioxide with carbon, to form additional carbon monoxide and reduce thecost of oxygen requirements. Thus, those skilled in the art nowunderstand the use of carbon dioxide to minimize the costly oxygenrequirement and to maximize the production of carbon monoxide.

[0057] Continuing the description of FIG. 1, the partially regeneratedspent cracking catalyst and the second atmosphere flow upwardly withinthe second regenerator dilute phase transport line 430 to the seconddisengaging space 410 for separation of a substantial portion of theremaining coke from the partially regenerated spent catalyst. Partiallyregenerated catalyst flowing from the upper portion of the secondregenerator dilute phase transport line 430 tends to fall into the lowerportion of the second disengaging space 410 to form a fluid bed. Whilelocated within the fluid bed, additional oxidation of the coke from thepartially regenerated catalyst may occur. To facilitate the additionaloxidation within the fluid bed, in an exemplary embodiment, additionaloxygen containing combustion gas may be introduced within the fluid bed.For example, the additional oxygen containing combustion gas may beintroduced within the fluid bed at a point below a distribution grid orpiping coil (not shown).

[0058] The vaporous reactants of the second regeneration zone 400 tendto rise within the second disengaging space 410 and enter the cyclones450. The cyclones 450, similar to the cyclones 250 found within thecatalytic cracking reaction zone 200, may separate suspended spentcatalyst from the vaporous flue gas. Spent catalyst removed from thevaporous flue gas may then flow downwardly through the dip leg of thecyclones 450 to the fluid bed, as the vaporous flue gas exits the secondregeneration zone 400 through the second regeneration zone flue gastransport line 440. The vaporous flue gas may then enter the secondregeneration zone treating or separation system 460. The vaporous fluegas may be given treatment or separation utilizing any one or more ofseveral types of well-known treatments or separations. Such treatments,if utilized, may separate the vaporous flue gas into its constituentcomponents. In contrast to the first regeneration zone 300 where largeramounts of carbon dioxide are formed, the second regeneration zone 400produces larger amounts of synthesis gas, such as carbon monoxide. Thisis a result of the higher temperatures used in the second regenerationzone 400 and in a partial oxidizing mode which conditions favor theformation of carbon monoxide rather than carbon dioxide. Other minorconstituents produced by the treatment of the vaporous flue gas includewater, sulfur compounds, nitrogen compounds, carbon dioxide andparticulate matter. It should be pointed out that, in contrast to theprior art systems, it has been found that the use of cooling coilswithin either the first or second regeneration zones 300, 400, simplyreduces the efficiency of the first and second regeneration zones 300,400, to maximize the production of carbon monoxide. For such a reason,it is preferred that cooling coils not be used within the first orsecond regeneration zones 300, 400.

[0059] In one particularly advantageous embodiment, high enough amountsof carbon monoxide are produced from the oxidizing of coke andalternatively supplemental fuels, if any, to fuel or feed other systemswithin the petrochemical plant, or be sold to an external enterprise.Regardless, using the above-mentioned process has turned what washistorically considered waste into a valuable and profitable resource.

[0060] In situations where the operator of the catalytic cracking system100 has entered into an agreement with an external enterprise to providea specified amount of carbon monoxide, and the coke formingcharacteristics of the feedstock are not great enough to provide theagreed upon quantity of carbon monoxide or hydrogen gas, supplementalfuel 675 may be included at most any point in the flow path of the spentcracking catalyst, with consideration of the hydrogen content andvolatile component content. Although the supplemental fuel 675 may beadded at any one of many points, it is preferred to add it to the spentcatalyst steam stripper 220 ahead of the first regeneration zone 300 soas to reduce the hydrogen content and/or volatile component content, ifany, of such supplemental fuel 675. Such carbon-based materials mayinclude carbon derived from coal, pitch, and many others. Furthermore,it is preferred to use a high carbon-based material having lowconcentrations of hydrogen, ash, and sulfur.

[0061] It should be noted that carbon monoxide may not be the only fluegas constituent produced in high enough quality or quantities forresale. In a preferred embodiment of the invention, carbon dioxide fluegas by-product or the carbon dioxide content thereof produced from thefirst regeneration zone 300, and carbon dioxide content of flue gasby-product produced from the second regeneration zone 400, is producedin a quantity sufficient to provide the carbon dioxide containing streamneeded in the second regeneration zone 400, and also provide anadditional quantity of carbon dioxide sufficient for resale. Hydrogengas content may also be recovered or produced from the secondregeneration zone 400 flue gas by-product for separate use or sale.Additionally, flue gas by-product (e.g., synthesis gas) from the secondregeneration zone 400 rich in carbon monoxide, may, external of theregeneration zone, be subjected to a classical water gas reaction toadjust the hydrogen content, provided that the reactant water vapor doesnot contact the cracking catalyst at the second regeneration zonetemperature. If this occurs, the carbon monoxide may react with thewater to form hydrogen content, and the hydrogen may thereafter beseparated for further use or sale.

[0062] Once the vaporous flue gas has been separated from thesubstantially regenerated catalyst, a portion of the hot substantiallyregenerated catalyst located within the fluid bed may be recycledthrough a hot recycle catalyst transport line 480 to the lower portionof the second regenerator dilute phase transport line 430, to increasethe initial temperature therein. However, the remaining portion of thenow regenerated cracking catalyst travels through the regeneratedcatalyst transport line 420 to the lower portion of the dilute phasecracking reactor transport line 230 to complete the cracking catalystcirculation. The net substantially regenerated catalyst would thenrecombine with the feedstock as previously mentioned, and the processwould repeat itself.

[0063] With reference henceforth to FIG. 2, a process of catalyticallycracking feedstock of high coke-forming characteristics and regeneratingthe spent cracking catalyst therefrom so as to produce synthesis gasusing a catalytic cracking system 105 is disclosed. Certain remarkablefeatures of the catalytic cracking system 105 of FIG. 2 include a secondregeneration zone 400 operated much as in FIG. 1, in the sametemperature range and in a partial oxidizing mode, but uniquelyutilizing a second species of catalyst effective in accelerating thepartial oxidizing reactions. This second species of catalyst may bemixed with spent cracking catalyst in the second regeneration zone 400alone or in the second and third regeneration zone 400, 500, as shown inFIG. 2. The second species of catalyst may be mixed with crackingcatalyst during regeneration and separated from the spent crackingcatalyst by any physical means, as it is done for example withoutlimitation by elutriation in FIG. 2 when the regeneration objective forthe respective regeneration zone has been achieved. In a preferredembodiment, a Group VIII metal, such as without limitations, cobaltand/or nickel content on an inorganic refractory support catalyst ofparticle size larger than the fluid cracking catalyst, may be used forformulation of the second species of catalyst. The skilled artisan willunderstand from the disclosed description of FIG. 2, how the use of asecond species of catalyst may also be effectively employed in a tworegeneration zone cracking process as well as with more than two suchregeneration zones. Those skilled in the art will understand how thesecond species of catalyst may be withdrawn from the regeneration zones400, 500, and regenerated in external equipment not show in FIG. 1 or 2,and then returned to the regeneration zone for maintaining highactivity. Further, those skilled in the art understand how water gasreactions may be conducted on synthesis gas product external of thecatalytic cracking system 100, 105, to adjust the hydrogen to carbonmonoxide mole ratio. The skilled artisan will further understand thatthe example of FIG. 2 describes the use of a second species of catalystfor a fluid catalytic cracking process, but this description will makeclear to such skilled artisan how to apply the teaching to othercatalytic cracking systems, such as without limitation, moving bedcatalytic cracking system. In FIG. 2 the second species of catalyst isused in conjunction with the partially regenerated spent crackingcatalyst so as to maximize the production of synthesis gas therein. Alsoshown in FIG. 2 is a third regeneration zone 500 which is operated in anoxidizing mode to restore maximum cracking catalyst activity.Additionally the third regeneration zone 500 may, as is shown in FIG. 2,receive (and return to the second regeneration zone) the second speciesof catalyst and to regenerate the second species of catalyst, restoringthe activity of the second species of catalyst by contaminant reduction,such as without limitations sulfur reduction, and providing a supply ofdry carbon dioxide rich gas for use in the second and third regenerationzones 400, 500 respectively, as well as for stripping partiallyregenerated cracking catalyst exiting the first regeneration zone 300.

[0064] The names of component parts of the catalytic cracking reactionzone 200 of FIG. 2, their respective identifying numbers, and thefunction of the component parts are the same as described in FIG. 1above except for the source of hot recycle catalyst to the catalyticcracking reaction zone 200. In FIG. 2 hot recycle catalyst to the dilutephase cracking reactor transport line 230 comes via the regeneratedcatalyst transport line 520, whereas in FIG. 1 the hot regeneratedcatalyst comes via the regenerated catalyst transport line 420.

[0065] With respect to the first regeneration zone 300, the names ofcomponent parts, the respective identifying numbers, and the functioningof the component parts is the same for FIG. 2 as was detailed above forFIG. 1, including the carbon dioxide rich stream stripping of thepartially regenerated spent cracking catalyst before introducing intothe second regeneration zone 400. For the second regeneration zone 400of FIG. 2, the names of component parts, the respective identifyingnumbers, and the functioning of the component parts is the same orsimilar to that given above for FIG. 1 except for differences necessaryto employ the second species of catalyst and to add to the catalyticcracking system 105 (FIG. 2) a third regeneration zone 500. The secondspecies of catalyst is added to the second regeneration zone 400 throughpiping not shown and for practical purposes its presence is maintainedin the second regeneration zone 400, and as shown herein, in the thirdregeneration zone 500. In FIG. 2 the mixture of spent cracking catalystand the second species of catalyst are admixed within the secondregenerator dilute phase transport line 430 and then at least partiallyseparated in the second disengaging space 410, while for exiting thesecond disengaging space 410 each species is segregated by elutriation.

[0066] Continuing the description of FIG. 2, the cracking catalystthereof has been substantially, but not completely, regenerated withinthe second regeneration zone 400. The substantially regenerated crackingcatalyst exits the second regeneration zone 400 via the second partiallyregenerated catalyst transport line 425. The second regeneration zone400 may be equipped with an internal collection trough 470 positioned ata higher elevation position within the second disengaging space 410 thanthe nozzle for hot recycle catalyst transport line 480. Accordingly,elutriation favors (not to the total exclusion) cracking catalystentering the internal collection trough 470 and thus the connectedsecond partially regenerated catalyst transport line 425 more than thesecond species of catalyst. The second species of catalyst is therebymore directed to circulate in the hot recycle catalyst transport line480 and the second regenerator dilute phase transport line 430, andreturn to the second disengaging space 410. The separation of the twodifferent species of catalyst is not intended to be exact because someof the second species of catalyst is intended to flow to the thirdregeneration zone 500 for subjection to oxidizing mode for oxidizationregeneration then return to the second regeneration zone 400. It shouldbe clear to the skilled artisan that the use of a second species ofcatalyst effective in promoting the partial oxidizing reactions(especially the reaction of carbon dioxide with at least a slight excessof carbon of the coke and supplemental fuel if used) is intended to aidin the formation of carbon monoxide, but the employment of the secondspecies of catalyst is at the discretion of the operator.

[0067] Partially regenerated spent cracking catalyst within the secondregeneration zone 400 flows through the second partially regeneratedcatalyst transport line 425 to the lower portion of the thirdregenerator dilute phase transport line 530 of the third regenerationzone 500. Here, the partially regenerated spent cracking catalystencounters a third atmosphere, comprising a third oxygen containing gas.At this lower portion of the third regenerator dilute phase transportline 530, hot catalyst from the third disengaging space 510 may be addedvia transport line 685 to increase the initial temperature of thereactants and to accelerate the final regeneration in an oxidizing mode.

[0068] In one advantageous embodiment, the third regeneration zone 500temperature is somewhat similar to the second regeneration zone 400temperature. For example, the third regeneration zone 500 temperatureshould also be greater than the 1400° F. used in the first regenerationzone 300. In an exemplary embodiment, the third regeneration zone 500temperature may range from about 1500° F. to about 1800° F. Since thewater forming hydrogen content of the coke was substantially reduced inthe first and second regeneration zones 300, 400, the partiallyregenerated spent cracking catalyst can handle temperatures up to about1800° F. without damage.

[0069] The cracking catalyst rises with the regeneration reactants inthe third regenerator dilute phase transport line 530 to the thirddisengaging space 510, entering in a downwardly direction to a fluid bedof mixed catalyst. A flow of the second species of catalyst is withdrawnin transport line 685 with a controlled portion flowing to the lowerportion of the third regenerator dilute phase transport line 530. Aregenerated second species of catalyst returns to the secondregeneration zone 400 via transport line 690. Vaporous reactants exitingthe upper level of the third regenerator dilute phase transport line 530rise to the upper level of the third disengaging space 510 and enter thecyclones 550. As has been pointed out for other regeneration zones, thecyclones are shown as two cyclones in series but may be internal,external, or mixed and may be any number in series, parallel, or mixed.Fully regenerated cracking catalyst from the third regeneration zoneexits via trough 570 and the regenerated catalyst transport line 520 toreturn to the catalytic cracking reaction zone 200 to complete thecirculation. Those skilled in the art will understand that thetemperature of the hot regenerated catalyst may be adjusted if needed.The net flow of the second species of catalyst, from the thirdregeneration zone 500 flows from the third disengaging space 510 throughtransport line 690 to the lower portion of the second regenerator dilutephase transport line 430 completing its circulation.

[0070] As used herein, the distinction between an oxidization mode ofoperation and a partial oxidization (sometimes called reduction) mode ofoperation in regeneration by combustion of hydrocarbonaceous materialfrom the surface of catalytic cracking catalyst is determined by thesystem operating temperature and by relative concentration of reactants,assuming through mixing.

[0071] An oxidizing mode of operation will exist where the systemoperating temperature is relatively low, for example without limitationless than a threshold temperature of about 1400° F. above whichthreshold temperature carbon dioxide reactant begins to significantlyreact with at least a slight excess of carbon to form carbon monoxide(coincidentally about the temperature above which conventional catalyticcracking catalyst is damaged by cindering in the presence of significantwater vapor), even if all significant oxygen reactant is consumed, andeven with an excess of carbon reactant remaining. While some synthesisgas components may be produced at these conditions, such synthesis gascomponents would be of reduced concentration and admixed withconcentrations of carbon dioxide as to be uninteresting except as lowcalorific value fuel and would cost almost as much to remove dilutingimpurities for chemical feedstock use as it would cost to produce thesynthesis gas of commercial quality from scratch. This operating mode isintended for use in the first regeneration zone described herein and theseverity of oxidization may be judged by analyzing the mole ratio ofcarbon monoxide to carbon dioxide (CO/CO2), which is for the most part afunction of operating temperature, as limited to a rather low number ator below 1400° F. by chemical equilibrium.

[0072] Where the operating temperature of the cracking catalystregeneration system of this application is above the thresholdtemperature where carbon dioxide will react with carbon, the relativeconcentration of reactants determine whether the system is in anoxidization mode of operation or in a partial oxidization mode ofoperation.

[0073] Where a regeneration system is operated above the thresholdtemperature and where carbon dioxide is added as a temperature limitingreactant to combine with carbon to form two moles of carbon monoxide,and where the amount of available oxygen reactant to the regenerationzone is less than a stoichiometric amount, (such term meaning hereinthat the oxygen input would be sufficient to combine with carbon contentto form carbon dioxide, with hydrogen content to form water, with sulfurcontent to form sulfur oxide, and with reactive nitrogen content to formnitrogen oxide) the system is in a partial oxidation mode. This typepartial oxidation mode of operation is intended herein for use in thesecond regeneration zone hereof, where carbon dioxide is introduced suchthat any excess heat rise of oxygen combining exothermically with carbonto form carbon oxide is balanced by carbon dioxide content reacting withcarbon endothermically to limit and control the temperature rise. Justas importantly, however, the reaction of carbon dioxide with carbonincreases the synthesis gas component production of carbon monoxide inaddition to controlling temperature. The molal ratio of carbon monoxideto carbon dioxide (CO/CO2) is used in part to judge the partialoxidation (reduction) severity of operation.

[0074] In a regeneration system operated above the threshold temperatureat or above which carbon dioxide will react with carbon, and where theamount of oxygen reactant to the regeneration zone is a stoichiometricamount as herein defined, or an even slightly greater amount, the systemis said to be in an oxidization mode of operation. This oxidization modeof operation exemplifies a third regeneration zone where a preferredembodiment uses a third regeneration zone. The flue gas from thisoxidizing mode of operation will be relatively water (moisture) free andof high carbon dioxide content, thus suitable for use in the second orthird regeneration zones or as a stripping gas for partiallyregenerated, spent cracking catalyst between the first regeneration zoneand the second regeneration zone.

[0075] The above-mentioned inventive method of producing a synthesis gasfrom regeneration of a spent cracking catalyst has many monetary andenvironmental benefits associated therewith. Of particular importance isthe ability of the current inventive method to convert the vaporous fluegas, which was historically considered waste, into usable andnon-environmentally objectionable material. Historically, the vaporousflue gas was passed through a waste heat boiler, treated, for examplefor reduction of sulfur compounds or particulate matter, and releasedinto the atmosphere, all the while raising environmental concerns.However, since the current process is capable of producing commercialamounts of synthesis gas, and that synthesis gas is captured, the amountof particulate matter (PM), sulfur oxide (SO_(X)), nitrogen oxide(NO_(X)) and volatile organic compounds (VOC) released into theatmosphere by the second regeneration zone 400 is substantially reduced.Moreover, not only are these emissions reduced, but they are reduced bypurification of product synthesis gas.

[0076] Another environmental and monetary benefit resulting from theinventive method of producing a synthesis gas from regeneration of aspent cracking catalyst, resides in the ability of the catalyticcracking system 100, 105 to accept heavier feedstock (long residuum),i.e., feedstocks containing high amounts of asphalt, pitch and otherhigh coke forming constituents, without the need to hydrotreat, distill,or extract such feedstocks prior to catalytic cracking. However, this isnot to say that some treatment may not still be profitable, for examplewithout limitations, hydrotreatment for metals content reduction.Currently, the quality of the crude oil derived feedstock has decreasedin recent years, and unless one is willing to pay a very high premium toget very high quality feedstock, heavy feedstock was the only option.However, as a result of the above-mentioned process, the catalyticcracking of heavy feedstock is now a plausible option.

[0077] Historically, using the high boiling feedstock requireddistilling, extracting, or hydrotreating of the long residuum, asphalt,pitch and other components of high coke forming characteristicfeedstock, prior to catalytically cracking such a feedstock. However,since the distillation process may, with the disclosed invention, bedispensed with for many crude oil sources, environmental and storageconcerns associated with the removal of the asphalt, pitch and otherhigh coke forming constituents are substantially reduced. Likewise, anyemissions into the atmosphere resulting from the hydrotreating,distillation or extraction processes are substantially reduced.Therefore, the ability to accept raw heavy feedstock is bothenvironmentally and momentarily beneficial.

[0078] Some reduction in the emissions from sources other than thecatalytic cracker may also be realized. Such possible sources mayinclude, in addition to hydrotreatment, distillation, and extractionprocessing equipment, the alternate conversion equipment, such as butnot limited to, coker processing equipment. Because the amount of longresiduum which is processed in such sources is substantially reduced oreliminated, the emissions of such sources would be reduced accordingly.Emissions such as fugitive emissions, however, are generally unaffectedunless the total operation is discontinued, although the shut down canbe part-time.

[0079] Another benefit realized by the inventive method, and morespecifically the higher production rate of synthesis gas, is that onlyabout 28% of the heat evolved in complete combustion mode ofregeneration is experienced in forming carbon monoxide in the catalystregenerators. The lower heat output of partial oxidization over completecombustion plays an important roll in maintaining the catalytic crackingsystem in thermal equilibrium, while continuing to remove enough of thecoke from the catalyst to sustain the cracking process.

[0080] Although the present invention has been described in detail,those skilled in the art should understand that they can make variouschanges, substitutions and alterations herein without departing from thespirit and scope of the invention in its broadest form. For example,those skilled in the art will understand that there are almost limitlessways that the process of FIG. 1 or FIG. 2 can be modified withoutdeparting from the teachings of the herein described invention.

What is claimed is:
 1. A catalytic cracking process, comprising:introducing at least one species of a natural or synthetic residuumfeedstock and a cracking catalyst into a catalytic cracker reactionzone; cracking said feedstock into a lower molecular weight gaseousproduct and spent cracking catalyst with hydrocarbonaceous productdeposited thereon; and regenerating said spent cracking catalystobtained from said catalytic cracker reaction zone, including;introducing said spent cracking catalyst into a first regeneration zonein a presence of a first atmosphere containing an oxygen containing gas,wherein said first regeneration zone is operated at a temperatureranging from about 1150° F. to about 1400° F. so as to reduce crackingcatalyst damage resulting from higher temperature regeneration with ahigh moisture content atmosphere, and so as to oxidize a greaterproportion of a hydrogen content than carbon content of coke associatedwith said spent cracking catalyst, thereby substantially reducing awater content of a subsequent regeneration zone; and introducing saidspent cracking catalyst from said first regeneration zone into a secondregeneration zone in a presence of a second atmosphere containing anoxygen containing gas and a carbon dioxide containing stream, whereinsaid second regeneration zone is operated at a temperature ranging fromabout 1500° F. to about 1800° F. and maintained in a partial oxidationmode, said second atmosphere, said second regeneration zone temperatureand said partial oxidation mode of operation resulting in a substantialportion of said carbon dioxide of said second atmosphere to function asa reactant with carbon remaining associated with said spent crackingcatalyst to form two moles of carbon monoxide per mole of carbon dioxidereacted, and thus result in a synthesis gas product rich in carbonmonoxide; and recycling said regenerated cracking catalyst to saidcatalytic cracker reaction zone.
 2. The method as recited in claim 1wherein said lower molecular weight gaseous product is rich in olefincontent.
 3. The method as recited in claim 1 wherein said lowermolecular weight gaseous product is rich in ethylene content.
 4. Themethod as recited in claim 1 wherein said lower molecular weight gaseousproduct is rich in propylene content.
 5. The method as recited in claim1 wherein said catalytic cracker reaction zone is a first catalyticcracker reaction zone and further including at least a second catalyticcracker reaction zone.
 6. The method as recited in claim 5 wherein atleast one of the first or second catalytic cracker reaction zones isdesigned to crack virgin residuum feedstock at an optimum crackingtemperature for the desired product.
 7. The method as recited in claim 5wherein at least one of the first or second catalytic cracker reactionzones is designed to crack recycled hydrocarbon feedstock from adownstream separation facilities of said catalytic cracker reactionzone, or from external operations, at an optimum cracking temperaturefor the desired product.
 8. The method as recited in claim 6 or 7wherein the products from the first or second catalytic cracker reactionzones are separated from their respective spent cracking catalyst forregeneration.
 9. The method as recited in claim 1 wherein a supplementalfuel is added to a flow path of said spent cracking catalyst.
 10. Themethod as recited in claim 1 wherein said synthesis gas product rich incarbon monoxide is introduced to a separate reaction zone external ofsaid catalytic cracking process for a classical water gas reaction inwhich the carbon monoxide reacts at least in part with added water vaporto form synthesis gas with adjusted hydrogen to carbon monoxide ratioand may be used or sold or separated and then used or sold.
 11. Themethod as recited in claim 1 further including introducing said spentcracking catalyst from said second regeneration zone into a thirdregeneration zone in a presence of a third atmosphere comprising a thirdoxygen containing gas, wherein said third regeneration zone is operatedat a temperature ranging from about 1500° F. to about 1800° F. andmaintained in an oxidation mode to produce a flue gas by-product rich incarbon dioxide.